IMO COLREG Rule 15

Rule 15 governs the crossing situation between two power-driven vessels: the vessel that has the other on her own starboard side must keep out of the way and, if circumstances permit, avoid crossing ahead of the other. The give-way vessel’s preferred action under Rule 8 is normally a substantial alteration to starboard to pass astern. The vessel with the other on her port side is the stand-on vessel under Rule 17 and holds course and speed until risk requires otherwise.